1. Field of the Invention
The present invention relates to electronics and communications. More particularly, the present invention relates to digital video systems.
2. Description of Related Art
In video on-demand (VOD) systems, digital compressed video and audio bitstreams are stored on a server and streamed out to a user's set top box or subscriber station. Over the course of the VOD session, many different streams are transmitted to a set top box to allow forward and rewind and other such features.
Typically, video must be streamed continuously to the set top box in order for it to operate properly, and video servers are designed to meet this requirement. However, servers are generally not able to switch between different streams at any precise point in the streams.
The resulting transitions seen by the user usually contain visual artifacts such as macroblocking, rolling, tearing, and shaking. Modifying the server to improve transitions is not an attractive option since it would add significant complexity and cost to the most expensive part of the VOD system.
One common method for handling stream transitions is to perform an operation analogous to a digital channel change by changing the packet identifier (PID) value that the set top box uses to identify the video that it should receive. While this technique may reduce or remove some of the visual artifacts, it does not eliminate all of them. Also, this method increases the delay incurred for the transition because the method requires that after the set top box is notified of the PID change, the set top box must flush its video buffer and wait while the video buffer is refilled. Also, the display to the user during the such a reset of the decoder buffer varies between set top vendors and models. Some set top boxes will freeze the last frame of the old stream while another may go to an entirely “black” frame.
Transition smoothing techniques generally are a tradeoff of latency (or delay), complexity, and visual quality. In addition, there are difficulties in achieving transition smoothing (or visual improvement of stream transitions) which is independent of set top box model.